1. Field of the Invention
The present invention relates to intake air control apparatus and method for an internal combustion engine in which an intake air quantity sucked into a cylinder of the engine and, more particularly, relates to the intake air control apparatus and method for the internal combustion engine in which an intake air quantity control is achieved by means of a variable control of a valve lift characteristic of an intake valve (or intake valves).
2. Description of the Related Art
An intake air quantity is controlled by means of an opening angle control of a throttle valve, generally, installed within an intake air passage. As is well known in the art, in such a kind of control method, a pumping loss is large during middle and low loads of the engine in which the opening angle of the throttle valve is, particularly, small (narrow). Such a trial that a lift quantity or valve open and closure timings of the intake valve are varied so that the intake air quantity is controlled independently of the throttle valve has heretofore been made. Utilizing this technique, in the same way as a Diesel engine, such a structure of a, so-called, throttle-less intake air quantity control apparatus in which the throttle valve is not equipped in an intake system has been proposed.
A Japanese Patent Application First Publication No. 2001-263105 published on Sep. 26, 2001 discloses variably operated valve mechanisms which can continuously vary a valve lift, a working angle, and a central angle of the valve lift of the intake valve. According to such kinds of variably operated valve mechanisms as disclosed in the above-described Japanese Patent Application First Publication, it is possible to variably control the intake air quantity flowing into the cylinder independently of the opening angle control of the throttle valve. Particularly, in a small load region, a, so-called, throttle-less driving or the driving with the opening angle of the throttle valve sufficiently largely maintained can be achieved. Consequently, a remarkable reduction of the pumping loss can be achieved.